Polyester multi-filamentary yarn for tire cords, dipped cord and production thereof

ABSTRACT

Disclosed are polyester multi-filamentary yarn useful as a reinforcement for tires and a dipped cord formed therefrom. The polyester multi-filamentary yarn comprises at least 90 mol % of polyethylene terephthalate and has an intrinsic viscosity of 0.70-1.2 and a tenacity of 5.5-8.5 g/d with an intermediate elongation difference (E1−E0) between intermediate elongations E0 and E1 amounting to 6% or greater. The polyester dipped cord is produced by subjecting at least two strands of polyester multi-filamentary yarn to first twisting and second twisting, the polyester multi-filamentary yarn comprising 90 mol % of polyethylene terephthalate; forming the strands into a fabric; and treating the fabric with blocked isocyanate and resorcinol formaldehyde latex (RFL), wherein the cord satisfies the following characteristics: a) a tenacity of 5.0 g/d or greater, b) a dimensional stability index (E 4.5 +SR) of less than 7.0%, c) a breaking elongation of 9% or greater, and d) an intermediate elongation difference (E1−E0) of 3% or less. Showing a harmony of high elastic modulus and low shrinkage, the filamentary yarn and dipped cords are superior in dimensional stability and fatigue resistance, so they can be used as reinforcements for rubber composites such as tires.

This application is a divisional of application Ser. No. 09/362,377,filed on Jul. 28, 1999, now U.S. Pat. No. 6,329,053 Dec. 11, 2001 theentire contents of which are hereby incorporated by reference and forwhich priority is claimed under 35 U.S.C. §120.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an industrial polyestermultifilamentary yarn of high modulus and low shrinkage, as areinforcement for tires, and a dipped cord formed therefrom. Moreparticularly, the present invention relates to a polyestermultifilamentary yarn which retains superior dimensional stability andfatigue resistance even at high temperatures and a dipped cord formedtherefrom. Also, the present invention is concerned with a method forproducing such a polyester multifilamentary yarn and a dipped cord.

2. Description of the Prior Art

One of the typical functional uses which fibers have is to reinforcerubber composites, such as tires. Examples of the fibers useful as sucha reinforcement include nylon, polyester, rayon, etc. Of them, polyesterfibers contain benzene rings in their molecular structure, exhibiting arigid property. Accordingly, tire cords produced from polyester yarnsshows high elastic modulus and few flat spots with superiority infatigue resistance, creep resistance and endurance. By virtue of thesehigh physical properties, polyester is extensively used as areinforcement for rubber composites, especially tires.

In spite of these advantages, conventional polyester tire cords sufferfrom a significant disadvantage of reducing the side wall indentation ofmonoply radial tires. Also, industrial polyester yarns are required toimprove in dimensional stability in order to replace the rayon fiberswhich have been applied for radial tires. In this regard, recentresearch has been directed to the development of polyester fibers whichhave high strength and elastic modulus in the same level as that ofrayon fibers.

Techniques for increasing thermal stability in polyester fibers arefound in, for example, U.S. Pat. Nos. 4,101,525 and 4,195,025 (both toDavis et al.) which disclose a polyester tire cord produced by drawinghighly oriented undrawn yarn in a high-speed spinning process under asteaming condition to give highly oriented drawn yarn, especiallymulti-drawn yarn containing at least 85 mol % of polyethyleneterephthalate, which ranges, in denier per filament, from 1 to 20 and,in work loss at 150° C., from 0.004 to 0.02 lb.in, and dipping themulti-drawn yarn in a rubber solution.

Another prior art relating to a tire cord can be acquired from JapanesePat. Laid-Open No. Sho. 61-12952 which discloses a process for producinga tire cord, comprising the steps of spinning a polyester having anintrinsic viscosity of 1.0, a diethylene glycol content of 1.0 mol %, acarboxyl group content of 10 eq/10⁶ g at a spinning speed of 2,000˜2,500m/min to obtain undrawn yarn, drawing the undrawn yarn at about 160° C.,thermally treating the yarn at 210˜240° C., and dipping the yarn in anordinary rubber solution. In this process, the temperature just below aspinning nozzle ranges from 100 to 450° C. The tire cord thus producedis, however, poor in physical properties. For instance, the tire cordranges, in absorption peak temperature in amorphous portions, from 148to 154° C. and, in dry shrinkage, from 3.3 to 5% with a tenacity of atleast 7.0 g/d.

Focusing on high tenacity and low shrinkage, as introduced above, theresearch which was made on the development of the filamentary yarn fortire cords provided methods in which undrawn yarn with a high quantityof orientation and crystallinity is produced through spinning at a highstress and endowed with high tenacity and low shrinkage propertiesthrough drawing at a high draw ratio.

The yarns produced by the high-speed spinning or drawing according tothe prior arts are improved in fatigue resistance, but problematic inthat the molecular chain lengths in amorphous portions are non-uniformand extend. As a result, relaxed molecular chains coexist, giving riseto a great loss in tenacity. Thus, the yarns suffer from significantdisadvantages of being poor in drawability owing to a large differencein physical properties between inner and outer layers of the yarn and ofexhibiting a great variation in physical properties owing to defects intheir micro structure. Moreover, the yarns produced from a highlyviscous polymer with an intrinsic viscosity of 1.0 or more show a limitof low shrinkage. Yarns which are drawn with a high orientation inadvance of undergoing a tire cord conversion process have a definitetwo-phase structure of crystalline and amorphous portions. Where thehighly oriented yarns are subjected to a thermal treatment by dipping ina rubber solution, deterioration is brought about in the crystallineportion with aggravation in the non-uniformity of the molecular chain,leading to a lowering of strength. As for polyester multi-filamentaryyarn, it is highly apt to be damaged because it undergoes a series ofafter treatment processes. For example, at least two strands of thedrawn yarn primarily obtained are subjecting to first and secondtwisting and formed into a fabric, after which the fabric is dipped in arubber solution and incorporated into a rubber matrix of a tire, andduring these processes, the yarn may be changed in physical propertiesand undergoes breaking of molecular chains.

SUMMARY OF THE INVENTION

Knowledge of the fact that, in order to use drawn polyester filamentaryyarn in tire cords, it is important to allow the drawn yarn to have auniform structure of molecular chains and the balance of high elasticmodulus and low shrinkage than to provide the drawn yarn with hightenacity and low shrinkage because the drawn yarn experiences seriousalteration in physical properties and molecular structure, leads to thepresent invention.

Therefore, it is an object of the present invention to overcome theabove problems encountered in prior arts and to provide polyestermulti-filamentary yarn for tire cords, which retains excellent thermalstability and fatigue resistance even after thermal aging.

It is another object of the present invention to provide tire cordsformed from such polyester multi-filamentary yarn.

It is a further object of the present invention to provide a method formaking such polyester multi-filamentary yarn for tire cords.

In order to approach the above objects, first, when making drawn yarn,factors causative of non-uniformity in the molecular chain structure ofthe yarn must be excluded to as much extent as possible and the balanceof high elastic modulus and low shrinkage is provided for the yarn.Next, the drawn yarn is allowed to undergo a uniform structural changein the course of the dipping process and even under the strictconditions of tire manufacturing processes, so that the resulting dippedtire cords are deformed as little as possible under a high temperaturecondition of the tires, i.e. tire rotation while the car is driving.Consequently, the tires are superb in endurability.

In other words, the factors which cause non-uniformity in the molecularchain of the yarn are minimized during the producing processes of thedrawn yarn while the parameters which are involved in the structuralchange of the molecular chains of the drawn yarn and dipped tire cordsare controlled in the dipping process and tire-manufacturing processes.

There are many factors which are causative of non-uniformity in themolecular chains of polyester yarn. For instance, in the course from themelting of a polyester resin to the step just before the extrusion ofthe molten polyester from nozzles, the intrinsic viscosity and meltingtemperature of the polyester resin have an influence on the molecularweight distribution of the molten polymer, together with the retentiontime which it takes for the molten polymer to flow to the nozzles. Uponextrusion of the molten polymer from the nozzle, the number and thediameter of the nozzles play an important role in determining theuniformity of the resulting yarn. In the processes after the extrusion,such as a quenching process and a winding process, quenchingtemperatures and winding speeds cause a structural change in both of theinner and outer layers of the yarn extruded from the nozzles(hereinafter referred to as “extruded yarn” ), thereby bringing about asignificant effect in the molecular chains of the inner and outerlayers. During the drawing of the extruded yarn by taking up, thecausative factors included the orientation and breakage of the molecularchain. Upon thermal treatment, the relaxation extent of the molecularchain is taken into account. Hence, the formation of a uniform structurein the molecular chain is affected by a variety of factors which aredistributed in various process steps from polymer melting through meltspinning, quenching (quenching temperature), and drawing to thermaltreatment. Since the factors are interconnective to each other, anappropriate combination of the factors is necessary to produce the drawnyarn which has a uniform structure of the molecular chain.

Fundamentally, in order to attain a uniform structure in the molecularchain, the processing conditions at the process steps which areimportant for the uniformity of the molecular chain are set in such amanner that the occurrence of the non-uniformity is minimized. Forinstance, it is preferable to minimize the retention time in the meltingand filtering steps of a polymer. The non-uniformity due to a suddenchange in a quenching step after spinning can be significantly reducedby converting the sudden change into a gradual one. Where thenon-uniformity of the molecular chain is due to drawing, it can besolved by conducting the drawing process at a low draw ratio. Inaddition, a thermal treatment stabilizes the molecular chain.

Accordingly, the present invention can be attained by satisfying theconditions of the problematic process steps simultaneously.

In accordance with an aspect of the present invention, there is provideda process for producing polyester filamentary yarn from a polyesterresin which comprises at least 90 mol % of polyethylene terephthalatewith an intrinsic viscosity of 0.7˜1.2, comprising the steps of: meltingthe polyester resin at a temperature of 290° C. or below; filtering themolten resin for a filtering retention time of 10 min or below;extrusion-spinning the filtered, molten resin through a nozzle which has250˜500 holes, each ranging, in diameter from 0.5 to 1.2 mm with alength/diameter ratio from 2 to 5; primarily quenching the extruded yarnat a temperature of 100˜195° C. in a zone of 50 mm or more distancedirectly below the nozzle; secondarily quenching the yarn with quenchair at its glass transition temperature (Tg) or below; taking off theyarn at a spinning stress of 0.3 g/d or greater; and drawing thetaken-off yarn at a total draw ratio of 1.3 or greater and thermallytreating the yarn at a temperature of 150˜230° C.

The term “filtering retention time” as used herein means the time ittakes for the molten resin to travel from the screw end of the extruderto the holes of the nozzle.

In accordance with another aspect of the present invention, there isprovided polyester filamentary yarn for tire cords, which comprises atleast 90 mol % of polyethylene terephthalate and has an intrinsicviscosity of 0.70˜1.2 and a tenacity of 5.5˜8.5 g/d with an intermediateelongation difference (E1−E0) between intermediate elongations E0 and E1amounting to 6% or greater. The intermediate elongation E0 is theelongation under a load of 4.5 g/d while the intermediate elongation E1is the elongation under a load of 4.5 g/d after conducting a thermaltreatment at 177° C. for 10 min under a load of 0.01 g/d. The yarnpreferably has an amorphous orientation function of 0.65 or greater anda terminal modulus of 15 g/d or below.

In accordance with a further aspect of the present invention, there isprovided a polyester dipped cord which is produced by twisting thepolyester filament yarn in at least two strands, forming the strandsinto a fabric, and treating the fabric with blocked isocyanate andresorcinol formaldehyde latex (RFL), wherein the cord satisfies thefollowing characteristics:

I) a tenacity of 5.0 g/d or greater,

ii) a dimensional stability index (E_(4.5)+SR) of less than 7.0%,

iii) a breaking elongation of 9% or greater,

iv) an intermediate elongation difference (E1−E0) of 3% or less.

DETAILED DESCRIPTION OF THE INVENTION

The present invent,on pertains to polyester filamentary yarn for tirecords, which is uniform in molecular chain and has a harmony of highelastic modulus and low shrinkage with superiority in dimensionalstability and fatigue resistance. Suitable for the production of thepolyester filamentary yarn according to the present invention is apolyester resin which contains at least 90 mol % of polyethyleneterephthalate and has an intrinsic viscosity of 0.7˜1.2 and preferably0.7˜0.9.

This resin was melted, filtered and spun by extrusion through a nozzle.The melting of tire polyester resin is conducted at a temperature ofless than 290° C., preferably at a temperature less than 288° C. andmore preferably at a temperature of 285˜288° C. During the filtration,the molten resin is treated for a filtering retention time of 10 min orless, preferably 8 min or less. As for the nozzle, it has 250˜500 holes,each ranging, in hole diameter, from 0.5 to 1.2 mm with a holelength/hole diameter ratio from 2 to 5.

Next, the extruded yarn is subjected to a primary quenching process inwhich the yarn passes through a quenching zone of 50 mm or more distancedirectly below the nozzle, maintained at a temperature of 100˜195° C.,so that the undrawn yarn is allowed to have a spinning stress of 0.3 g/dor higher.

Subsequently, a secondary quenching process is conducted, in which theextruded yarn is solidified by quenching with quench air at thepolymer's glass transition temperature or less.

Thereafter, the undrawn yarn is drawn at a temperature between the Tgand the crystallization temperature of the polymer.

Finally, the drawn yarn is thermally treated at a temperature of150˜230° C.

The polyester filamentary yarn of the present invention preferablycomprises polyethylene terephthalate at a content of 90 mol % and morepreferably 95 mol %. Correspondingly, other copolyesters thanpolyethylene terephthalate may be contained at an amount of 10 mol % orless and preferably 5 mol % or less.

In addition to polyethylene terephthalate, useful copolyesters in thepresent invention may be produced from glycols, such as diethyl glycol,trimethylene glycol, tetramethylene glycol and hexamethylene glycol, anddicarboxylic acids, such as isophthalic acid, hexadihydroterephthalicacid, adipic acid, cebasic acid and azellaic acid.

The polyester filamentary yarn of the present invention, usually has afineness of 3˜5 deniers per filament, but these values can be varied ina wide range as is apparent to the skilled in this art.

Where the polyester filamentary yarn of the present invention isincorporated as a reinforcing fiber into a rubber composite such as atire, the yarn allows the rubber composite to show excellent dimensionalstability and toughness. Therefore, the polyester filamentary yarn canefficiently replace the rayon fibers which have recently been used inmonoply radial tires. Further, it is expected that the polyesterfilamentary yarn of the present invention will meet the requirements fora further improvement in the dimensional stability of polyester.

First, when a cord is excessively shrunk during a curing process, aremarkable reduction is brought about in the elastic modulus of thecord. Second, the shrinkage of the cord is closely concerned with theuniformity of the tire. In practice, accordingly, the comparison ofelastic modulus at high temperatures with dry shrinkage is regarded asvery important in tire cords. An intermediate elongation E_(4.5) (anelongation under a load of 4.5 g/d) and an E_(4.5) growth after the freeshrinkage (aging) at a certain sulfurizing temperature are used asmeasures of compliance. Of the factors to determine the controllabilityof tires, the elastic modulus at high temperatures is one of the mostimportant parameters.

The polyester multi-filamentary yarn of the present invention consiststypically of 200˜500 continuous filaments with a fineness of 3˜5 deniersper filament, but these values may vary in a large range.

When being applied for dipped cords, the multi-filamentary yarn of thepresent invention is comparable with rayon, which is usually used as areinforce material of tires. Particularly, the multi-filamentary yarn ofthe present invention is useful as an industrial fiber by virtue of itshigh tenacity and toughness even in a high temperature condition of 100°C. or greater and low shrinkage.

Suitable as the starting material for the production of themulti-filamentary yarn of the present invention is a polyester which hasan intrinsic viscosity (η) of 0.7˜1.2 and preferably 0.7˜0.9. Theintrinsic viscosity may be calculated from the following equation bydetermining the relative viscosity (η_(r)) of a solution of 8 g of asample in 100 ml of ortho-chlorophenol at 25° C., using an Oswaldviscometer. η = 0.042  η_(r) + 0.2634$\eta_{r} = \frac{t \times d}{t_{0} \times d_{0}}$

wherein

t=dropping time of solution (sec),

t₀=dropping time of ortho-chlorophenol (sec)

d=density of solution (g/cm³) and

d₀=density of ortho-chlorophenol (g/cm³)

Since the polymerization quantity of a polymer, if it is a kind of amolecular weight, has the same concept as intrinsic viscosity, thepolymerization quantity is closely connected with the conformationalstability and fatigue resistance of the polymer. In detail, the lowerthe molecular weight of a polymer is, the more advantageous the polymeris in terms of conformational stability. On the other hand, as a polymerhas a higher molecular weight, the polymer is more advantageous infatigue resistance. In the present invention, an excellentconformational stability is secured by use of a polymer which has arelatively low intrinsic viscosity ranging from 0.7 to 1.2.Simultaneously, the degradation in fatigue resistance was minimized byspinning the polymer at such a temperature of 288° C. or less andparticularly, 285˜288° C. as to prevent the reduction of its molecularweight.

The spinning nozzle useful in the present invention has 250˜500 holes,in total, each of which has a diameter of 0.5˜1.2 mm and preferably0.8˜1.0 mm and a length/diameter ratio of 2˜5 and preferably 3˜5. Wherea spinning process is carried out in the manner of 2Cop winding after 4ends spinning, the number of holes preferably ranges from 120 to 250 perone end. In this case, doubling is conducted after quenching. For theone-shot spinning in which 2Cop winding is performed after 2endsspinning, 250˜450 holes preferably exist in one nozzle.

In order to obtain highly oriented, undrawn yarn, it is important toraise the spinning stress of the undrawn yarn to 0.3 g/d or higher. Thisis affected by the magnitude of the tension which the extruded yarnundergoes upon reaching the glass transition temperature by cooling withquench air. In turn, the magnitude of tension depends on the spinningspeed, the discharge quantity of per opening, the temperature of theatmosphere just below the nozzle, and the temperature of the quench air.

Hence, the tension of the undrawn yarn is determined in the point wherethe extruded yarn from the spinneret reaches a temperature below theglass transition temperature by cooling with quench air. In the presentinvention, there is provided a technique of heightening the spinningspeed to increase the speed of tensile deformation of the extruded yarnin addition to raising the spinning stress even at the same spinningspeed by controlling the temperature of the atmosphere just below thenozzle. In addition to minimizing the frequency of cut or broken fibers,this technique allows the raising of the spinning stress of the undrawnyarn, leading to the production of highly oriented, undrawn yarn.

In accordance with the present invention, the extruded yarn is primarilycooled in a quenching zone of 50 mm or more distance directly below thenozzle, preferably in a quenching zone extending from a 50 mm-distantpoint to a 250 mm-distant point from the nozzle, more preferably from a50 mm-distant point to a 150 mm-distant point, which is maintained at atemperature of 100˜195° C., preferably 100˜180° C. and more preferably100˜150° C.

Typically, a shroud which heats the atmosphere just below the nozzle tothe nozzle temperature or higher is set to reduce the orientationquantity of the undrawn yarn, so as to achieve high draw ratios at whichthe undrawn yarn is drawn to produce yarn of high tenacity. However, theresulting yarn suffers from high thermal shrinkage. If the spinning isconducted at a high speed while keeping the shroud at high temperaturesin order to improve the dimensional stability, a steep deformationalgradient is brought about in the polymer, frequently causing fiber to becut or broken and giving rise to a sudden decrease in the productionefficiency.

After completion of the primary cooling process, the filamentary yarn issubjected to a secondary cooling treatment with quench air. The coolingis preferably carried out at a temperature of 20° C. to the glasstransition temperature of the polymer and preferably 40˜50° C. In thetemperature range, the temperature difference the inner and outer layersof the filament at the solidification point can be reduced. Accordingly,a tenacity reduction attributable to the structural difference betweenthe inner and outer layers of the filament can be minimized. Inaddition, alleviating the deformational gradient of the polymer improvesits spinning property, so that the molten polymer shot from the nozzleby spinning under a high stress condition has an alleviateddeformational gradient, thereby minimizing the non-uniformity ofphysical properties and the occurrence of broken filaments.

If non-uniformity happens in the filament upon quenching, a significantdecrease in the tenacity of the yarn is caused after drawing, making itvirtually impossible to achieve an excellent dimensional stability aswell as high tenacity by use of low viscosity polymers.

In the present invention, the undrawn yarn thus obtained is wound insuch a manner that the yarn has a spinning stress of 0.3 g/d or greaterand more preferably 0.5˜0.8 g/d. The winding is conducted at a speed of2,500 m/min or higher and more preferably 2,700˜3,500 m/min.Subsequently, the wound yarn is drawn at a low draw ratio and at atemperature ranging from the glass transition temperature to thecrystallization temperature of the undrawn yarn.

A multi-step drawing process is preferably used in the presentinvention. Since the crystallization temperature of a highly orientedundrawn yarn produced by a high-speed spinning process is usually lowerby 10° C. or more than that of an undrawn yarn obtained by a low-speedspinning process, the drawing temperature is preferably adjusted to arange of 120° C. or below, more preferably 70˜120° C. and mostpreferably 70˜100° C. For example, if the drawing temperature exceeds120° C., fine crystals are already formed before the orientation of themolecular chains, degrading the drawability of the yarn and, in anextreme case, breaking the molecular chains. On the other hand, if thedrawing is conducted at a temperature less than 70° C., the molecularchains lose their mobility so that the drawing efficiency is lowered.with the aim of providing the yarn with a tenacity of at least 5.0 g/d,the total ratio is controlled to be in the range of 1.3:1˜2.0:1 andpreferably 1.3:1˜1.6:1. For example, where the total draw ratio is below1.3:1, the resulting fiber is poor in tenacity. On the other hand, ifthe ratio is over 2.0:1, high modulus values and low shrinkage cannot beattained with a high percentage in tenacity reduction.

As for the multi-step drawing process, the drawing is preferablyconducted so as to achieve about 70% or less of the total draw ratio inthe first drawing zone. For example, if more than 70% of the total drawratio is accomplished in the first drawing zone, the period of timewhich it takes for the tangled molecular chairs to attain a fibrillarstructure is so short that parts of the molecular chains still remaintangled. Serving as a structural defect, the tangled molecular chainsgives rise to an increase in thermal shrinkage.

In the present invention, advantage is taken of the characteristicproperties of the highly oriented undrawn yarn produced by thehigh-speed spinning process, e.g., the properties in which the undrawnyarn is transformed into a liquid-like form rather than undergoesshrinkage when it is thermally treated under a specific condition afterthe drawing, so as to greatly decrease the shrinkage of the dipped cord.

The elongation and shrinkage behavior upon heat application can bethought to result from the difference of elongation power due to thecrystallization of the oriented amorphous molecular chains. Accordingly,the present invention utilizes the mechanism of the elongation andshrinkage behavior in minimizing the shrinkage.

The intensive and thorough research, repeated by the present inventors,resulted in the finding that, in order to maximize the water-likeelongation behavior, crystallization by heat should not occur during thedrawing. To this end, the drawing is conducted at a temperature lowerthan the crystallization temperature of the undrawn yarn and at a lowdraw ratio. In the case that crystallization by heat occurs, in advance,in the drawing process, the oriented amorphous portions are transformedinto crystalline portions and therefore, the elongation transformationwhich usually occurs as the oriented amorphous portions are changed tooriented crystals no longer occurs. There occurs only the shrinkagebehavior ascribed to the disorientation of the amorphous molecularchains which are present in the amorphous portions, leading to anincrease of dry shrinkage.

A characteristic of the present invention is to thermally treat thedrawn yarn. Because the yarn whose orientation is almost completelyfinished is subjected to thermal treatment, the structure of the yarn isdependent greatly on the temperature. The thermal treatment is carriedout at a temperature of 150˜230° C. and preferably 150˜180° C. Forexample, if the temperature is higher than 210° C., there exists a cleardiscrimination between the amorphous portions and the crystallineportions, so that the orientation quantity of the crystalline portionsis extremely increased while the amorphous portions are decreased. As aresult, the degradation of physical properties due to abnormal crystalgrowth cannot be minimized in a subsequent dipping process. Upon thethermal treatment, the yarn may be relaxed at a quantity of 2% orgreater.

In general, the undrawn yarn attains the characteristic properties ofthe finally produced yarn as a consequence of the crystallization andorientation of molecular chains when the undraw yarn undergoes a drawingprocess. The orientation in the course of the drawing takes place inboth of the crystalline and amorphous portions and the drawing tensionof the amorphous portions are higher than that of the crystallineportions.

According to the method of the present invention, there can be producedfilamentary yarn which has an intrinsic viscosity of 0.70˜1.2 andpreferably 0.7˜0.9, a tenacity of 5.5˜8.5 g/d and more preferably5.5˜7.5 g/d with an intermediate elongation difference (E1−E0) betweenintermediate elongations E0 and E1 amounting to 6% or greater,preferably 6˜15% and more preferably 6˜10%.

Because of the interconnection among the above properties, thefilamentary yarn must satisfy all of the properties in order to afford atire cord which exhibits the desirable characteristics. In particular,the intermediate elongation difference (E1−E0), which is one of the mostimportant indexes to inform the uniformity of the molecular chainsduring the production of the drawn yarn, must be in a range of 6% orgreater with which the molecular chains continue to be uniformly changedin subsequent dipping and tire-manufacturing processes. In this range,the molecular chain structure of the drawn yarn is converted into auniform one in the dipping process which is executed at a hightemperature under a tension condition. If the difference E1−E0 is lessthan 6%, non-uniformity may be brought about in the molecular chainstructure when the dipping process is carried out at a high temperatureunder a high tension condition.

As high as 0.65 in the amorphous orientation function (fa) of the yarnallows the yarn to be improved in tenacity in the dipping process. Morepreferably, the yarn has an amorphous orientation degree (fa) of0.65˜0.8. In addition, in order to bring about a more uniform molecularchain in the yarn in the dipping process, it is preferable to set theterminal modulus of the yarn in a range of 15 g/d or below.

Most of the accumulated stresses in the yarn are attributed to the heatwhich is used in the drawing and thermal treatment. In order to reducesuch stresses, the orientation quantity of the amorphous portion wasdecreased to 0.6 as disclosed in U.S. Pat. Nos. 4,101,515 and 4,195,052.Even in this case, however, constrained amorphous molecular chainscannot be sufficiently released owing to the folded molecular chains onthe crystal surface and a large amount of defects on the crystalinterface, and it is not easy to obtain high elastic properties due tothe decrease of the proportion of tie molecules.

The filaments according to the present invention are twisted in morethan two strands on the basis of a fineness of 1,000˜2,000 deniers andformed into a fabric, after which the fabric is dipped in a conventionaladhesive solution such as RFL (resorcinol-formaldehyde-latex). Afterbeing dried, the dipped fabric is thermally treated at a certaintemperature under a tension condition, followed by normalizing thefabric to give dipped cord cloth. The term “dipped cord” as used hereinmeans the warp cord constituting the dipped cord cloth. In the dippedcord cloth, the weft serves only to secure the distance between the warpcords. Therefore, the characteristics of dipped cord cloth arerepresented mainly by those of the warp cord. The same is true of thepresent invention.

The tire cord which is obtained by use of the filament of the presentinvention has a dimensional stability index of 7% or less and preferably6%, a tenacity of 5.0 g/d or greater and preferably 5.5˜7.5 g/d, and abreaking elongation of 9% or more, and more preferably 15˜20% with theintermediate elongation difference E1−E0 amounting to 3% or less,preferably 2% or less and more preferably 1% or less.

As retaining excellent dimensional stability and fatigue resistance evenunder a high temperature condition, the dipped cord of the presentinvention can be applied for rubber composites, such as tires.

The physical properties described above were measured according to thefollowing methods:

tenacity and elongation: samples 250 mm long were tested at a tensilespeed of 300 mm/min under the atmospheric conditions of 25° C. and 65%RH by use of a low-speed elongation type tensile strength tester,commercially available from Instron Co., Ltd., in accordance with JIS-L1017 (1983).

intermediate elongation of yarn (E_(4.5)): the elongation value at aload of 4.5 g/d on an elongation load curve obtained by use of thetensile strength tester in accordance with JIS-L 1017. E0 is anintermediate elongation under a load of 4.5 g/d while E1 is anintermediate elongation under a load of 4.5 g/d after a thermaltreatment for 10 min at 177° C. under a load of 0.01 g/d.

intermediate elongation growth: E1−E0.

intermediate elongation of dipped cord and its growth: the sameprocedure as in the yarn was repeated.

terminal modulus of yarn: on a tenacity-elongation curve, the increaseof the tenacity (ΔT(g/d)) between a braking elongation (E(%)) and acertain point (E-2.4) is obtained. A terminal modulus is calculated fromthe following equation.${{Terminal}\quad {Modulus}\quad ({Mt})} = {\frac{\Delta \quad T}{2.4 \times 10^{-}2}\quad \text{(g/d)}}$

dry shrinkage of cord (SR): the value calculated from the followingequation wherein I_(o) was the length of the cord fabric measured undera dead weight load of 20 g after it was placed at 25° C., 65% RH formore than 24 hours and I₁ was the length after it was placed in an ovenat 150° C. for 30 min under a dead weight load of 20 g.${{SR}\quad (\%)} = {\frac{l_{0} - l_{1}}{l_{0}} \times 100}$

thermal stability index: the intermediate elongation plus the dryshrinkage of cord.

amorphous orientation function (fa): calculated from the followingequation (1): $\begin{matrix}{{fa} = \frac{{\Delta \quad n} - {{x_{c} \cdot f_{c} \cdot \Delta}\quad n_{c}}}{\left( {l - x_{c}} \right)\Delta \quad n\quad a}} & (1)\end{matrix}$

 where

Δn_(c)=intrinsic birefringence of crystal (0.220)

Δn_(a)=intrinsic birefringence of amorphous (0.215). The birefringence(Δn) may be calculated from the following equation (2) by measuring theretardation obtained from the interference fringe by the sample using aBerek compensator mounted in a polarizing light microscope,

Δn=R/d  (2)

 where

d=thickness of sample (nm)

R=retardation (nm).

crystallinity (Xc): determined from the following equation using thedensity (ρ, unit: g/cm³) of the yarn.$x_{c} = \frac{\rho_{c}\left( {\rho - \rho_{a}} \right)}{\rho \left( {\rho_{c} - \rho_{a}} \right)}$

 where,

ρc (g/cm³)=1.445

ρa (g/cm³)=1.335

The density (ρ) may be determined by measurements according to densitygradient column method using n-heptane and carbon tetrachloride at 25°C.

spinning stress: measured between an oiling device and a first godetroller with the aid of a tension meter.

A better understanding of the present invention may be obtained in thelight of the following examples which are set forth to illustrate, butare not to be construed to limit the present invention.

EXAMPLES 1 TO 5 AND COMPARATIVE EXAMPLES 1 TO 4

Polyester chips with an intrinsic viscosity of 0.65, which were preparedby solid polymerization, were melt-spun through a spinneret whichcontained 300 holes (hole diameter 0.60 mm) under the conditionsindicated in Table 1, below. The molten resin were filtering forfiltering retention time of 8 min. A shroud 200 mm long was placedimmediately below the spinneret to provide various temperatureconditions as shown in Table 1. In a quenching zone, solidification wasperformed wit secondarily quenching air of 40° C. which moved at a speedof 0.6 m/sec while the undrawn yarn was taken off at a speed of 3,000m/min. Subsequently, the undrawn yarn was drawn in a two-step drawingprocess at 80° C. and 100° C. (total draw ratio 1.60 times) using agodet roller. On the godet roller, the yarn was thermally treated atvarious temperatures as indicated in Table 1. While being relaxed at aquantity of 2%, the yarn 1,000 deniers in fineness was wound on awinder.

The physical properties of the yarn obtained from each example wereshown in Table 2, below.

Two strands of the yarn obtained from each examples were subjected tofirst twisting and second twisting, respectively, at 480 TPM and dippedin RFL at 245° C. to give dipped cords. The physical properties of thedipped cords are shown in Table 3, below.

TABLE 1 Primar- Thermal- ily ly Intrin. Spinning quenching Springtreated Nos. of Viscos. Temp. Temp. of undrawn Temp. Exemp. of Chips (C)(C) yarn (g/d) (C) Exmp. 1 0.75 282 100 0.35 190 Exmp. 2 0.75 282 1900.32 190 Exmp. 3 0.85 284 150 0.42 200 Exmp. 4 0.85 284 195 0.40 200Exmp. 5 0.95 288 150 0.55 200 C.Exmp. 1 0.70 295 250 0.25 230 C.Exmp. 20.95 300 250 0.34 230 C.Exmp. 3 0.95 300 320 0.32 230 C.Exmp. 4 1.10 305320 0.41 230

TABLE 2 Amorph. Intermed. Break. Term. Orient. Intrin. Elong. Nos. ofTenac. Elong. Modul. Degree Viscos. Growth Exmp. (g/d) (%) (g/d) (fa) ofyarn % Exmp. 1 5.8 15.8  2.5 0.81 0.71 11.8 Exmp. 2 5.8 15.5  2.0 0.780.70 13.2 Exmp. 3 7.0 16.0 12.0 0.75 0.82 10.5 Exmp. 4 7.0 16.0 10.80.69 0.82 8.1 Exmp. 5 7.0 15.8 12.9 0.75 0.92 6.9 C.Exmp.1 5.4 12.9 26.60.62 0.64 4.2 C.Exmp.2 6.8 12.2 32.0 0.64 0.88 5.7 C.Exmp.3 6.9 12.532.8 0.64 0.88 5.3 C.Exmp.4 7.5 12.3 34.9 0.63 0.95 4.8

TABLE 3 Physical Prop. of dipped Cords Intermed. Nos. of tenacity Elong.Exmp. (g/d) E_(4.5) SR ES Growth % Remarks Exmp. 1 5.2 3.5 2.3 5.8 2.6 —Exmp. 2 5.2 3.5 2.5 6.0 2.3 — Exmp. 3 6.2 3.5 2.8 6.3 2.6 — Exmp. 4 6.23.5 3.0 6.5 2.8 — Exmp. 5 6.3 3.5 3.1 6.6 3.0 — Exmp. 1 4.7 3.5 3.0 6.53.8 Greatly Exmp. 2 5.3 3.5 4.0 7.5 5.6 reduced Exmp. 3 5.5 3.5 4.0 7.55.3 yarn Exmp. 4 5.9 3.5 4.3 7.8 5.2 tenacity

Taken together, the data obtained in the examples and comparativeexamples demonstrate that the filamentary yarn and dipped cords of thepresent invention show a harmony of high elastic modulus and lowshrinkage in addition to being superior in dimensional stability andfatigue resistance. Consequently, the filamentary yarn and dipped cordsof the present invention can be used as reinforcements for rubbercomposites such as tires.

The present invention has been described in an illustrative manner, andit is to be understood the terminology used is intended to be in thenature of description rather than of limitation. Many modifications andvariations of the present invention are possible in light of the aboveteachings. Therefore, it is to be understood that within the scope ofthe appended claims, the invention may be practiced otherwise than asspecifically described.

What is claimed is:
 1. A polyester dipped cord cloth, which is producedby subjecting at least two strands of polyester multi-filamentary yarnto first twisting and second twisting, to form a twisted cord, saidpolyester multi-filamentary yarn comprising 90 mol % of polyethyleneterephthalate; forming the twisted cord into a fabric; and treating thefabric with blocked isocyanate and resorcinol formaldehyde latex (RFL),wherein the cord treated with RFL satisfies the followingcharacteristics: a) a tenacity of 5.0 g/d or greater, b) a dimensionalstability index (E_(4.5)+SR) of less than 7.0%, c) a breaking elongationof 9% or greater, and d) an intermediate elongation difference (E1−E0)of 3% or less, wherein the intermediate elongation E0 is the elongationunder a load of 4.5 g/d and the intermediate elongation E1 is theelongation under a load of 4.5 g/d after conducting a thermal treatment177° C. for 10 min. under load of 0.01 g/d.
 2. A polyester dipped cordcloth as set forth in claim 1, wherein the tenacity ranges from 5.5 to7.5 g/d.
 3. A polyester dipped cord as set forth in claim 1, wherein thedimensional stability index is in a level of 6% or less.
 4. A polyesterdipped cord as set forth in claim 3, wherein the breaking elongation isin a level of 15-18%.
 5. A polyester dipped cord as set forth in claim1, wherein the intermediate elongation difference E1−E0 is in a level of2% or less.
 6. A polyester dipped cord as set forth in claim 5, theintermediate elongation difference E1−E0 is in a level of 1% or less.